Prepregs, i.e. solid mixtures made of a reactive synthetic resin and a reinforcing material, in particular in fiber form, are an indispensible intermediate product in the production of composite materials, in particular fiber-composite materials; the increasing importance of these in numerous branches of industry, for example in aerospace technology, energy production by wind turbines, and construction of bicycles, rail vehicles, and ships is based on their exceptional combination of properties including relatively low weight and exceptionally high strength. These properties make it increasingly possible to use these composite materials successfully instead of high-density materials such as metals, despite higher production costs. Associated with this there is also the desire to maximize efficiency of production of these composite materials, and in particular to keep the cost of auxiliary production materials as low as possible.
Usually, the production of fiber-composite materials is carried out in a plurality of process steps whereby the resultant intermediate products sometimes require prolonged storage.
In this production of composite materials, prepregs are often the first intermediate product that is sometimes not stored at the premises of the producers of the final products, e.g. the producer of aircraft components, rotor blades for wind turbines, etc. Accordingly a requirement during intermediate storage either at the premises of the producer of the prepregs or at the premises of the processor of the prepregs to end products is therefore that the properties of the prepregs are not affected, and that problems by handling the prepregs during the final processing are minimized.
Therefore, when prepregs are produced by combining the reactive synthetic resin, as binder, with the reinforcing material to give a solid mixture, for purposes of protection and problem-free further processing of the prepregs said mixture is applied to a paper which has been siliconized at least on one surface and which can optionally be replaced by a polyethylene release film in the form of removable protective and release film. For numerous prepreg compositions it is moreover essential to equip both surfaces of a prepreg web with release paper or a removable polyethylene film in the form of release film, in order to guarantee problem-free further processing and storage.
Before the final processing of the prepregs, i.e. before final shaping thereof, said release films have to be removed, since the design and property profile of certain end products requires that a plurality of prepregs are combined. Since most processes for the final processing of fiber-composite materials have now been automated in order to maximize precision in the moldings, it is necessary to avoid any process problems due for example to break-off of the release films during their necessary removal. It is moreover desirable, in order to increase production efficiency, to minimize the extent of auxiliary materials that cause waste, and of removal thereof.
It was therefore an object of the present invention to provide a composite which is made of a prepreg and of a removable release film, which does not have the disadvantages of the prior art.